Book review: 'The Science of Kissing' by Sheril Kirshenbaum

It's not love so much as it is hormones, genes and propagating the species. Happy Valentine's Day.

It's late at night and you're finishing a truly golden date. You drank Manhattans and discovered that you both geek out about B-horror films and the collected works of Philip K. Dick. To top it off, you can't stop staring into each other's eyes. When you finally lean in for a kiss you feel a shock of gooey warmth and your heart pumps molasses.

The moment is terribly romantic. Too bad the same can't be said of the kiss itself. In her new book, "The Science of Kissing," Sheril Kirshenbaum dissects the kiss with a scalpel, peeling back its glamorized skin to reveal its sociopathic nature.

And we learn, that despite its exalted status as one of the world's most passionate activities, the kiss has evolved for a single blind purpose: to get you into bed so you can propagate the species.

Throughout the book, Kirshenbaum asserts that the best science experiment is the kind that defies your expectations. And so it is with the kiss itself. To best illustrate this point the book is divided into three parts. The first explores the origin of kissing, the second digs into how it affects you physiologically and the third finds the writer in an NYU laboratory trying to make new discoveries about kissing.

Kirshenbaum is a research scientist at the University of Texas at Austin and her writing is best when she's discussing the empirical. So although the information in part one about the kissing, sniffing and licking practices of our ancestors is interesting, it falls flat compared with part two.

It's when Kirshenbaum slogs through saliva, looking for clues to human attraction in tastes, hormones and smells, that she gets to third base.

In a particularly fascinating passage she describes how humans smell each other in intimate proximity in part to detect a group of genes called the major histocompatibility complex (MHC). MHC genes basically control the effectiveness of our immune systems. The more diverse our MHC is, the more likely our offspring are to have healthy immune systems.

In 1995 a researcher named Claus Wedekind conducted an experiment that became known as the "sweaty T-shirt experiment."

By getting 44 men to wear T-shirts without deodorant for two nights and then having women sniff them, Wedekind discovered that "women nearly always preferred the scents of T-shirts worn by men with MHC genes different from their own — suggesting that we can determine our genetic compatibility with potential partners simply by following our noses."

There is one curious exception to our attraction to different immune systems: women on the birth control pill tend to favor men whose MHC closely resembles their own. The science on why this occurs is sketchy but there's likely a fitting parable about why it's wise to not mess around too much with nature.

After all nature has evolved the kiss over millions of years so that humans can collect an overwhelming amount of complicated information that helps them determine the suitability of a mate to procreate with. We even taste each other's hormones. Men's saliva, for example is loaded with testosterone, which raises a woman's libido, "priming her for sex."

That's why researchers have found that men favor deep, sloppy kisses more than women do. Touching tongues "is a way to legally slip her a natural sex stimulant," writes Kirshenbaum in one of her wittier passages.

When Kirshenbaum embraces the titillating subject matter with an earthy Henry Miller sense of sexual joie de vivre, "The Science of Kissing" shows flashes of greatness, but all too often she veers back into family friendly territory. And sadly, for such wet subject matter, the book reads a bit dry.

Still, if you've ever wondered why you can't stop obsessing over a person after you first fall hard (it's the dopamine); or why certain couples manage to maintain stable, loving relationships for decades (thank you, oxytocin); or if you've worried about catching a lover's cold (humans are arguably "99 percent bacteria") you're sure to glean some remarkable and enlightening factoids from this book.

And don't worry — your newfound knowledge won't ruin the joy of kissing if you don't let it. Just close your eyes, open your mouth and try not to think about your date's genes. The kiss will do that for you.